Gonzalez-Ojeda, Roberto
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Gonzalez-Ojeda, Roberto
Official Name
Gonzalez Ojeda, Roberto
Alternative Name
robglez
González-Ojeda, R.
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ORCID
Scopus Author ID
56314856300
Researcher ID
DTL-2716-2022

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Structural Ultrafine Grained Steels Obtained by Advanced Controlled Rolling

2013 , Gonzalez-Ojeda, Roberto , García García, José Ovidio , Barbés Fernández, Miguel Ángel , Quintana, María José , Verdeja González, Luis Felipe , Verdeja González, José Ignacio

Steels with ultrafine grains (lower than 5 μpa), which usually known as ultrafine ferrite or ultrafine grained materials, are presently the object of intense research, because of the improvement in resistance and fracture toughness they may reach compared to conventional steels (with grain sizes above this value). It is shown that the forenamed steels designated in the Euronorm EN 10149-2, which are manufactured by advanced techniques of controlled rolling and mainly used in automotive industry, have an ultrafine grain size in the range of 2. 5 to 3. 5 μm, and with elastic yield stresses higher than 400 MPa. Based on the Morrison-Miller criterion, it is shown that values of the strain-hardening coefficient lower than 0. 08 would make the industrial application of these steels unfeasible.

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Nodal wear model: corrosion in carbon blast furnace hearths

2003 , Verdeja González, Luis Felipe , Gonzalez-Ojeda, Roberto , Alfonso, A. , Barbés Fernández, Miguel Ángel

Criterions developed for the Nodal Wear Model (NWM) were applied to estimate the shape of the corrosion profiles that a blast furnace hearth may acquire during its campaign. Taking into account design of the hearth, the boundary conditions, the characteristics of the refractory materials used and the operation conditions of the blast furnace, simulation of wear profiles with central well, mushroom and elephant foot shape were accomplished. The foundations of the NWM are constructed considering that the corrosion of the refractory is a function of the temperature present at each point (node) of the liquid metal-refractory interface and the corresponding physical and chemical characteristics of the corrosive fluid.

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Thermal modelling of a torpedo-car

2005 , Verdeja González, Luis Felipe , Barbés Fernández, Miguel Ángel , Gonzalez-Ojeda, Roberto , Castillo, G. A. , Colás, R.

A two-dimensional finite element model for computing the temperature distribution in a torpedo-car holding pig iron is described in this work. The model determines the temperature gradients in steady and transient conditions whiting the different parts that constitute the systems, which are considered to be the steel casing, refractory lining, liquid iron, slag and air. Heat transfer within the main fluid phases (iron and air) is computed assuming an apparent thermal conductivity term incorporating the contribution from convention and radiation, and it is affected by the dimensions of the vessel. Thermal gradients within the constituents of the torpedo-car are used to calculate heat losses during operation. It was found that the model required the incorporate of a region within the iron-refractory interface to reproduce thermographic data recorded during operation; the heat transfer coefficient of this interface was found to be equal to 30 Wm''-2K''-1.

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Effect of pressure in the microstructure of die cast Al-8.5Si-3.5cu alloys

2014 , Barbés Fernández, Miguel Ángel , Verdeja González, José Ignacio , Quintana, María José , Verdeja González, Luis Felipe , Gonzalez-Ojeda, Roberto

The microstructure of Pressure Die Casting of an Al-8.5 Si-3.5 Cu alloy used for clean room tiles shows amount of constituents (eutectic and Si phases) that do not correspond to the ones indicated by the phase diagram. Furthermore, there are differences in amount of constituents between the core and the surface zones of parts produced by this process. The work presents quantitative microstructural analysis of this type of industrially produced part, and as a possible cause for these differences, simulations of the effect of pressure on the eutectic (temperature and chemical composition) in the Al-Si system. As the production rate of these parts is very high, and solidification is very fast, microstructural heterogeneity may be related to local entrapment of gasses unable to escape during casting.

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Microstructures of a pressure die cast Al-8.5%Si-3.5%Cu alloy

2017 , Barbés Fernández, Miguel Ángel , Quintana, María José , Verdeja González, José Ignacio , Gonzalez-Ojeda, Roberto

Quantitative microstructural measurements of constituents of an Al-Si-Cu alloy, used to manufacture a part with thin sections by Pressure Die Casting (PDC), do not correspond to phase diagram calculations. A simulation of the liquid velocity when filling the mold was made in order to understand the relation between this parameter and pressure, cooling rate and the eutectic amount and morphology. Also, the microstructures of the same alloy solidified in a ceramic crucible (low cooling rate) and in a metal flask (high cooling rate) were compared to those obtained by PDC to analyze the role of pressure on the displacement of eutectic composition and formation of different eutectic morphologies. The amount of constituents varies with distance from the mold walls, producing higher or lower pressure zones, which may be estimated from the Al-Si phase diagram simulation at different pressures. As these pressures must be very high (∼ 2 GPa), a possible explanation for the displacement of the eutectic point is the combination of high cooling rate of the manufacturing process, entrapment of gases during solidification and influence of the alloying elements.

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Ultrafine Grained HSLA Steels for Cold Forming

2010 , Gonzalez-Ojeda, Roberto , García García, José Ovidio , Barbés Fernández, Miguel Ángel , Quintana, María José , Verdeja González, Luis Felipe , Verdeja González, José Ignacio

The industrial level production of ultrafine grained (or ultrafine ferrite) ferrous alloys was investigated through three examples of steels that complied with the EN 10149-2 Euronorm and were produced by advanced controlled hot rolling techniques. The steel samples were tension tested and chemically analyzed, and the microstructure was evaluated through quantitative metallographic techniques to determine parameters such as yield stress, amount of microalloying elements, strain hardening coefficient, grain size, and grain size distribution. These steels were micro-alloyed with Ti, Nb, and Mn with ASTM grain sizes of approximately 13–15. The careful control of chemical composition and deformation during production, giving a specific attention to the deformation sequences, austenite non-recrystallization temperatures and allotropic transformations during cooling, are indispensable to obtain steels with an adequate strain hardening coefficient that allows cold working operations such as bending, stretching or drawing.

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The Nodal Wear Model (NWM) as an Alternative to Understand the Mechanisms of Flow and Wear in the Blast Furnace Crucible

2010 , Gonzalez-Ojeda, Roberto , Barbés Fernández, Miguel Ángel , Verdeja González, Luis Felipe , Ruiz Bustinza, Íñigo Eloy , Mochón Muñoz, Javier , Duarte, Ramón Martín , Karbowniczek, Mirosław

The presence of thermocouples in the lining of crucibles has become a general practice in the new construction of blast furnaces. The Nodal Wear Model (NWM) has also emerged as an instrument that, while using experimental data, obtains nodal variables whose experimental measurement is not possible: global coefficient of pig-iron/refractory heat transfer h pig−iron/lining g−i and nodal temperature Ti . Starting from these nodal properties, the wear of the lining or the growth of scabs may be controlled, independently of the mechanisms responsible for them. In the same way, the properties and influence zone of the dead man in the hearth of the blast furnace may be calculated, along with those regions where the fluid is allowed to move without any other restrictions than the ones of the corresponding viscous flow (raceway hearth region).

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